.NET/Java PDF, Tiff, Barcode SDK Library

So, one row was successfully inserted into T and we duly received the message I fired and updated 1 rows. The next INSERT statement violates the integrity constraint we have on T. The DBMS_OUTPUT message appeared the trigger on T in fact did fire and we have evidence of that. The trigger performed its updates of T2 successfully. We might expect T2 to have a value of 2 now, but we see it has a value of 1. Oracle made the original INSERT atomic the original INSERT INTO T is the statement, and any side effects of that original INSERT INTO T are considered part of that statement. Oracle achieves this statement-level atomicity by silently wrapping a SAVEPOINT around each of our calls to the database. The preceding two INSERTs were really treated like this:

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In this chapter, you saw how you can use F# to perform a range of web programming tasks. You started by using sockets and TCP/IP to implement a web server directly, an example of a system network programming task. We then described how ASP.NET can be used to implement web applications involving HTML and input server controls and how to use embedded scripts and code-behind files. We also showed how you can access a database using F# Linq and display data coming from this database. You then looked briefly at web applications that incorporate significant client-side scripting using F# Web Tools and finally took a quick look at how to use web services from F#, including making compositional asynchronous invocations of web services. Data access is a topic that complements web programming and often forms a major part of server-based web applications. In the next chapter, you will look at how to access relational databases from F# programs and also at other aspects of working with data from F#.

Savepoint statement1; Insert into t values ( If error then rollback to Savepoint statement2; Insert into t values ( If error then rollback to

1 ); statement1; -1 ); statement2;

oftware applications deal with data in a wide array of forms: single values such as integers or strings; composite values paired together as tuples, records, or objects; collections of smaller pieces of data represented as lists, sets, arrays, or sequences; XML strings with tags describing the shape and kind of data; or data coming from relational or object-oriented databases, just to name a few In this chapter, we look at ways of working with some common data sources: In 3 you saw that sequences, similar to other enumerable data types such as lists, arrays, maps, and sets, have various aggregate iteration, query, and transform operators We first look at how these operators can be used in a straightforward manner to form SQL-like operations over in-memory collections This mechanism can be further tuned and applied to other data sources where the original data source is mapped to a sequence.

For programmers used to Sybase or SQL Server, this may be confusing at first. In those databases exactly the opposite is true. The triggers in those systems execute independently of the firing statement. If they encounter an error, the triggers must explicitly roll back their own work and then raise another error to roll back the triggering statement. Otherwise, the work done by a trigger could persist even if the triggering statement, or some other part of the statement, ultimately fails. In Oracle, this statement-level atomicity extends as deep as it needs to. In the preceding example, if the INSERT INTO T fires a trigger that updates another table, and that table has a trigger that deletes from another table (and so on, and so on), either all of the work succeeds or none of it does. You don t need to code anything special to ensure this; it s just the way it works.

It is interesting to note that Oracle considers PL/SQL anonymous blocks to be statements as well. Consider the previous stored procedure and reset example tables: ops$tkyte%ORA11GR2> create or replace procedure p 2 as 3 begin 4 insert into t values ( 1 ); 5 insert into t values (-1 ); 6 end; 7 / Procedure created. ops$tkyte%ORA11GR2> delete from t; 0 rows deleted. ops$tkyte%ORA11GR2> update t2 set cnt = 0; 1 row updated. ops$tkyte%ORA11GR2> commit; Commit complete. ops$tkyte%ORA11GR2> select * from t; no rows selected ops$tkyte%ORA11GR2> select * from t2; CNT ---------0 So, we have a procedure we know will fail, and the second INSERT will always fail in this case. Let s see what happens if we run that stored procedure: